Turbine rotor heat treatment process

Abstract

A method of heat treating a turbine rotor disk to obtain different radial properties at different locations in the rotor disk includes a) heating the rotor disk for a period of from 4 to 10 hours at a temperature of 1800° F.; b) cooling the rotor disk to a temperature of about 1550° F.; c) holding the rotor disk at about 1550° F. for a period of from about 2 to about 4 hours; d) cooling the rotor disk to room temperature; e) precipitation aging the rotor disk by heating the rotor disk to temperature of 1325° F. for 8 hours, holding it at 1150° F. for 8 hours, and f) cooling the rotor disk.

Description

BACKGROUND OF INVENTION [0001] This invention relates to heat treatment of turbine components and specifically, to a heat treatment schedule for achieving different properties at different locations in a nickel base superalloy turbine rotor disk. [0002] Generally, it is known that differential heat treatment of an object can be employed to impart different properties at different locations. However, while such treatment works well on cylindrical objects, it is difficult to implement on more complex shapes such as found in turbine wheels or disks. [0003] Alloy 706 is a nickel-based superalloy used for high temperature applications in gas turbines. This alloy can be used in connection with two heat treatment conditions identified by the inventor of the alloy (International Nickel Company) in the 1960's. The two known heat treatment processes are as follows: [0004] Heat Treatment A. [0005] Solution treatment at 1700-1850° F. for a time commensurate with section size, then air cool; [00...

AI Technical Summary

Benefits of technology

[0015] This invention uses a relatively simple but controlled heat treatment process whereby a turbine rotor disk will develop the required properties at the required locations.

[0016] This means that the outer diameter and the surface of the disk will have good creep and crack growth resistance, while the interior and bore will have high strength at temperatures below 750° F. The process can be implemented easily at facilities with standard industrial furnaces and does not require complicated fixtures. Furnace control and timing are critical but are of the kind available in most modern furnaces.

[0019] By controlling time at stabilization temperature, it is possible to have the outer diameter and surface exposed to 1550° F. for the right time to get good creep crack growth resistance and creep properties while the bore and inside surface of the part will be exposed to shorter times at this temperature and therefore have higher strength.

Problems solved by technology

However, while such treatment works well on cylindrical objects, it is difficult to implement on more complex shapes such as found in turbine wheels or disks.

If Heat Treatment A is used, the strength at the bore is not adequate, and if Heat Treatment B is used, there is not enough creep resistance at the high temperatures.

No process exists, however, to develop different properties at different locations in the complex shape of a turbine rotor wheel or disk.

This heat treatment process will impart good rupture and crack growth resistance, but will have poor strength at low and intermediate temperatures.

The '353 patent discloses modification of the composition for improved hot ductility at temperatures above 1300° F. The '494 patent modifies the process to achieve high strength at temperatures above 1300 F. The '323 patent describes a process of manufacturing a turbine disk using the Heat Treatment B but does not address the problem of creep and accelerated crack growth at temperatures above 900° F.

While the treatments described in certain of these patents (the '478, '353 and '494 patents) improve some properties at high temperatures, they do not also improve strength at low and intermediate temperatures.

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